(1) Field of the Invention
The present invention relates to a golf club, and more particularly, to the type of golf clubs commonly known as "irons".
(2) Description of the Related Art
In golf, the term "slice" means that when a ball is hit by, for example, a right-handed player, the trajectory of the ball in flight is greatly deviated to the right with respect to the intended straight line of flight. In general, players, especially beginners, are liable to slice the ball when using an iron club, and this tendency to slice becomes more pronounced as a shaft of the iron club becomes longer.
A cause of slicing by players, especially beginners, is their tendency to swing the iron club from the "outside-in", i.e., the orbit of the downswing of the iron club passes across the ideal swing line from the outside to the inside.
For this reason, there is a demand for an iron club and a set of iron clubs which will enable players, especially beginners, to avoid the "outside-in swing" when using an iron club, that is, will enable them to swing an iron club in an ideal, i.e., straight line, orbit.
FIG. 1 shows an example of a head of a conventional iron club, generally designated by a reference 10. The head 10 includes a neck 12 integrally formed therewith and connected to a shaft 14. The head 10 is provided with a face 16 having a scored zone on which score lines 18 are formed in parallel with a sole 20 of the head 10, and which is in contact with the ball when the ball is hit by the head 10. When addressing the ball before swinging, the head 10 is oriented so that the sole 20 thereof is parallel with the ground, and when the ball is struck by the scored zone of the face 16, a back spin is imparted to the ball by the score lines 18, which run parallel to the sole 20 and thus the ground.
As shown in FIG. 1, the scored zone of the face 16 on which the score lines 18 are formed is defined by boundary lines B.sub.1 and B.sub.2. As is well known, the boundary lines B.sub.1 and B.sub.2 may be formed in many different ways. For example, the scored zone may be distinguished from the other zones of the face 16 by using different materials for the scored zone and the other zones, so that the boundary lines B.sub.1 and B.sub.2 clearly differentiate the scored zone and the other zones. As another example, the scored zone may be subjected to a surface treatment which is different from that applied to the other zones, thereby forming the boundary lines B.sub.1 and B.sub.2 between the scored zone and the other zones. Furthermore, the boundary lines B.sub.1 and B.sub.2 can be formed as grooves between the scored zone and the other zones.
Conventionally, the boundary lines defining the scored zone are formed on the head face in a direction perpendicular to the head sole, as exemplified in FIG. 1. With this arrangement of the boundary lines, when a player using the iron club having a conventional head as shown in FIG. 1 addresses the ball, the player will see the boundary lines as lines not extending in parallel with the straight line passing through the center of the ball. In particular, the boundary lines will appear to extend obliquely from left to right with respect to the above straight line. Of course, if a spectator observes the head from a point just above the ball while the player is addressing the ball, the spectator will see the boundary lines extending in parallel with the straight line.
To hit the ball without slicing, the player must swing the club in a straight line, as mentioned above. However, with the arrangement of the boundary lines of the conventional head face, the player, especially a beginner, is liable to move the club on the backswing so that the club head is moved in a direction designated by the boundary lines which appear to extend obliquely from left to right with respect to the straight line, and thus the downswing of the club will be in the "outside-in" manner. This tendency becomes more pronounced as the club shaft becomes longer, since, to the player, the boundary lines will appear to extend more and more obliquely from left to right with respect to the straight line as the club shaft becomes longer.
An iron club having a longer shaft also provides another cause of slicing. Namely, the resilience of the club shaft allows it to bend at the beginning of a downswing of the club due to the inertial mass of the club, especially the head thereof. As the club shaft becomes longer, this bending becomes greater and thus the club head hits the ball before the club shaft is restored from the bent condition to a straight condition. In other words, the club head may hit the ball in an "open face" manner, thereby causing the player to slice the ball.
It is possible to prevent the club head from hitting the ball in the "open face" manner by delaying the timing of the impact of the club head with the ball until the club shaft has straightened, so that the head face is square to the ball at the moment of impact. The timing of the impact of the club head with the ball can be adjusted by varying a relative position of a leading edge of the club head with respect to the club shaft. In particular, by increasing an offset distance between the leading edge of the club head and an axis of the club shaft, or a goose distance between the leading edge of the club head and a leading side of the club shaft or the neck, it is possible to delay the impact timing so that the club head will hit the ball squarely. However, there are no conventional sets of iron clubs wherein the offset distance or the goose distance has been regulated in response to a length of the club shafts for adjusting the timing of the impact of the club head with the ball.
Another factor which causes slicing by players, especially beginners, is their tendency to bring the club head into contact with the ball at a point outside of a sweet point and toward a toe of the club head, which causes a rotation of the club head around the center of gravity thereof upon impact with the ball. This rotational movement of the club head is also a cause of slicing.
Yet another cause of slicing by players, especially beginners, is that their grip on the iron club may be too loose, and thus the club is allowed to rotate within the hands of the player when the club head hits the ball. This rotational slippage of the club in the hands of the player is also a cause of slicing.